1. Field of the Invention
The present invention relates generally to the field of power tools. In particular the present invention relates to a depth of cut adjustment arrangement for a router. More particularly, it relates to a router depth of cut adjustment employing a threaded ring.
2. Discussion
Various types of power tools comprise a cutting tool or bit that is raised or lowered relative to a base that rests on or against the workpiece. Often the tool or bit is attached to the output shaft of a motor unit that can be vertically or axially moved relative to the base. Movement of the motor unit and attached tool bit relative to the base unit determines the depth of cut into the workpiece.
Routers, including some laminate trimmers, are constructed according to this basic design. The router bit is attached to the motor output spindle by means of a tool holder such as a collet or chuck and the bit projects through an opening in the base to contact the workpiece. The motor unit is mounted to the base by means that allow the operator to move the motor and bit axially relative to the base in order to determine the depth of cut of the bit.
Router base and depth of cut systems fall into two commonly recognized categories. They are plunge base routers and fixed base routers (including so-called D-handle bases). Generally speaking, plunge routers comprise a generally planer base element, a motor unit, and a plurality of support columns on which the motor unit is vertically movably mounted above the base. Usually, the motor unit is biased upward or away from the base. Means are provided for finely adjusting the depth of cut and for locking the motor unit at the selected depth/height against the biasing force.
Fixed base routers usually comprise a generally cylindrical base and a motor unit with a cylindrical housing portion. The cylindrical portion of the motor housing fits snugly but movably within an annulus of the cylindrical portion of the base with the motor spindle and router bit projecting downward beyond the lowest portion of the base. The cylindrical portion of the base often includes a longitudinal or axial cut or gap that permits the base diameter to expand or contract slightly under the force of a clamp mechanism that bridges the gap and that can be used to tighten the base onto the motor housing within. Means for adjusting the depth of cut by adjusting the vertical or axial position of the motor unit and bit within the base are also provided. The base clamp is loosened for adjusting the cutting depth and after the desired depth is set with the depth adjusting means the base clamp is tightened to lock the motor housing at the set position.
One known means for adjusting the depth of cut in a fixed base router employs a rack and pinion arrangement. A toothed rack is attached in the axial direction on the exterior of the motor housing while a pinion is attached to the base so as to engage the pinion. Means, such as a knob, are provided for the operator to turn the pinion. Turning of the pinion drives the rack and the attached motor and bit. See for example U.S. Pat. No. 3,466,973 to Rees.
Another well known means for adjusting the depth of cut consists essentially of providing threads on the exterior of the motor unit and matching threads on the base assembly. Screwing the motor unit into and out of the base assembly raises and lowers the motor and cutter like a nut in a bolt. See for example U.S. Pat. No. 1,899,833 to Sacrey and U.S. Pat. No. 2,562,143 to Godfrey et al. Among several disadvantages of this means for adjusting the depth of the router is that the rotation of the router power head within the base assembly is problematic due to the presence of the power cord connected to the motor, which tangles or interferes with the rotation of the motor unit.
A refinement on the threaded motor unit concept is the replacement of a fully threaded base with a threaded ring or nut rotatably mounted on the base element. In such a mechanism, the ring can be manually rotated to raise and lower the power head relative to the base element without relative rotation between the motor unit and base element. See for example U.S. Pat. No. 2,988,199 to Godfrey et al. In some embodiments according to this concept means are provided to restrain the motor from turning within the base. These restraining means can take the form of an axial groove within the annulus of the base that is slideably engaged by a stud or projection on the exterior surface of the motor housing or vice versa. The engagement of the projection and the groove prevents the motor housing from turning within the base.
In some of these ring designs the ring merely rests atop the base element. This presents a problem, however, if the router is inverted. When inverted, the ring and the motor unit will tend to fall out of the base element unless the base clamp, if provided, has been sufficiently tightened to hold the motor by compression. When a router is mounted upside down in a router table, it is necessary to loosen the base clamp to adjust the depth of cut, then, unless additional connecting structure is provided, the problem remains of the motor and ring falling out of the router base.
In a further refinement, the ring can be rotatably connected with the base element so that it can retain and raise or lower the power head even when inverted. See U.S. Pat. No. 2,842,173 to Turner and U.S. Pat. No. 5,613,813 to Winchester et al. A disadvantage of a ring that is permanently axially connected to the base is that it prevents quick removal of the motor unit. Instead the motor must be unscrewed from the ring and base assemblyxe2x80x94usually requiring numerous turns of the ring to fully raise and free the motor housing. Quick and easy removal of the motor unit is desirable for convenient access to the motor spindle and collet/chuck when changing router bits. The inability of a fixed ring to quickly release the motor forces design choices between steep thread pitches of approximately 2 inches per revolution or greater, which can lower and raise and free the motor quickly, and fine thread pitches of approximately xc2xd inch per revolution or less, which provide greater depth control, but require numerous turns to raise and free the motor.
In another variation, the Porter-Cable Model 310 laminate trimmer employs a ring that is held axially atop the cylindrical base by means of a pair of steel leaf spring clips. See FIG. 13. Th clips 140 are mounted to the exterior of the base 120 and engage a v-shaped circumferential groove 136 around the outer side of the depth adjustment ring 130. So constructed, the ring 130 is axially secured to the base 120, but the motor using 114 and ring can be quickly detached and removed from the base.
Due to their small size, sharp edges, orientation and stiffness, the thin steel leaf spring clips 140 of the Porter-Cable Model 310 are extremely difficult to manipulate and do not appear to have been designed with the intention that the tool user actually operate them with his fingers. In practice, the Model 310 motor 114 is removed from the base 120 by a pull on the motor sufficient to overcome the compression force of the clips 140 engaged in the ring groove 136. Thus, the leaf spring clips 140 act rather as a mere detent mechanism that the motor 114 and ring 130 can be pushed in and pulled out of with only modest force. After adjustment of the depth a cut the base is tightened on the motor with a base clamp, as described above.
Laminate trimmers are essentially, however, very small routers. The motors of laminate trimmers are of less than one horsepower and usually draw less than 5 amps. Such small motors usually weigh less than five pounds. Furthermore, laminate trimmers are not usually used inverted and are not intended for mounting upside down in router tables. For such small lightweight routers that are infrequently inverted, the Model 310 clips provide satisfactory retention of the ring and motor with convenience of removal.
Regular, fixed based, wood working routers, however, have motors of approximately 1 to 3 or more horsepower, draw 5 to 10 or more amps, and weigh 5 or more pounds. Construction professionals and woodworking hobbyists frequently use such routers upside down and want to be able to mount them inverted under a router table for prolonged periods. The Model 310 ring system, however, does not scale up well to retain and operate these larger and heavier motors. The leaf spring clips do not exert sufficient compressive force to hold the ring and heavy motors against the force of gravity and the occasional shock. Moreover, as mentioned above, the size, sharp edges, orientation and stiffness of the Model 310 leaf springs clips make them difficult to manipulate, so that in practice the motor and ring are pulled out of the base with the clips serving as a detent. Furthermore, the structure of the Model 310 clips do not permit the user to loosen the clips with one hand while grasping the motor or base with his or her other hand.
It is, therefore, one object of the invention to provide a tool with an axial depth of cut adjustment arrangement that both securely retains the motor unit in the base when inverted, but also provides for quick and convenient release of the motor from the base.
It is another object of the invention to provide a retaining mechanism with exposed and graspable elements that will permit the tool user to release the motor from the base by operation of those elements with one hand.
It is still another object of the invention to provide a fixed base router with a threaded depth adjustment ring that can be selectably detachable from the router base.
This and other objects of the invention are attained by a fixed base router, with a height adjustment ring that is in turn removably attached to the base by a manually operable clip. The clip is large enough and resilient enough to retain the motor unit of a large router when inverted and can be manually released.
Because of the provision of a convenient mechanism for release of the motor from the base, another object of the invention is the identification of thread pitch for the motor housing and depth adjustment ring that provides an optimal compromise between fine and accurate depth control and quick and convenient gross adjustment depth adjustment.